Generally, the capsules for infusion products comprise a cup made of a plastic material, within which the infusion product is arranged, and a lid, also made of plastic material and arranged so that it closes the cup. The peripheral edge of the lid is welded to the upper edge of the cup by means of an apparatus of a known type, e.g. for generating ultrasounds, which carries out the welding by means of vibrations. When the capsule is inserted inside a percolation chamber of a machine dispensing drinks, hot water is injected under pressure and passes through at least one hole pierced in the lid to be mixed with the infusion product inside the cup. Then the drink comes out of the cup through at least one hole pierced in the bottom wall of the cup. In some percolator machines the capsule is arranged so that the hot water enters through the hole pierced in the bottom wall of the cup and leaves through the hole pierced in the lid.
The aforesaid capsules have a plurality of drawbacks.
In particular, during the percolation step, the upper edge of the cup is pressed between an upper body and a lower body defining the percolation chamber. In spite of this pressure, the percolation chamber does not guarantee a perfect hydraulic seal and therefore a portion of the injected water leaks out of the percolation chamber, exactly through the space defined between the two bodies of the percolation chamber pressing the upper edge of the cup between them. In order to improve the hydraulic seal, some producers use layers made of different materials to be glued on the upper and/or the lower face of the edge of the cup.